Pump, and an apparatus incorporating the pump for infusing liquid medicine

ABSTRACT

The pump has a chamber in which a piston reciprocates to pump a liquid. The piston is moved by having secured thereto the armature of at least one electromagnet (preferably two). The coil of the electromagnet is suitably external of the pump casing. A control circuit pulses the electromagnet at a predetermined rate to provide a predetermined periodic output. 
     In a preferred form, the pump is mounted together with a liquid reservoir on a printed circuit board, and the unit is encapsulated for implantation in the human body to infuse a liquid medicine at a controlled rate into the bloodstream.

This invention relates to a pump and to an apparatus incorporating sucha pump for infusing into a subject determined quantities of liquidmedicine at pre-determined time intervals.

The invention has particular, but not exclusive, relevance to medicalapplications in which controlled doses of drugs must be administeredover long periods of time. For instance, persons suffering from diabetesmelitus require routine administration of insulin, which is normallygiven by self-injection. Not only does this raise problems ofmaintaining supplies of sterile needles and the like, but the use ofinjections tends to limit administration to once or twice daily, and theresulting concentration of insulin in the blood fluctuates widely.

In this and other applications, there is a need for a means of infusingdrugs at a controlled rate so as to give relatively small amounts atrelatively frequent intervals, say one to four times per hour. Suchfrequency would preclude conventional injection.

Objects of the invention is therefore to provide a pump suitable for usein such infusion, and an infusion apparatus incorporating the pump.

According to the first aspect of the present invention, I provide a pumpcomprising a casing defining an elongate chamber, inlet and outletvalves communicating with the chamber, a piston coaxially movable in thechamber, and an electromagnet controlling movement of the piston via anarmature, the outlet valve also being controlled by the electromagnetvia a valve armature;

characterised in that the inlet and outlet valves are balls made from amaterial having ferromagnetic properties and seats made of non-magneticmaterial and magnets tensioning the balls of said inlet and outletvalves against their seats when in a closed position, and in that powermeans for opening said balls from their seats, comprise for said inletvalve a force equivalent to a hydraulic force caused by coaxial movementof the piston in the chamber, said piston and said outlet valve beingoperated against the flow of liquid by the excitation of the singleelectromagnet, a piston lock magnet providing a biasing force on thepiston thereby to inhibit unintentional movement of the piston, and saidoutlet valve remaining closed in response to adverse inlet or outletpressure conditions to prevent inadvertent flow of liquid.

According to a second aspect of the present invention, I provide anapparatus for infusing into a subject determined quantities of liquidmedicine at pre-determined time intervals, the apparatus comprising apump in accordance with the preceding paragraph in combination with areservoir, the pump further including at least one non-return valve forpassing liquid pumped from the reservoir to a cannula for infusing theliquid into a subject, and the circuitry including timing means foractuating the piston at predetermined regular intervals.

Preferably, two electromagnet coils are wound around the casing of thepump.

Preferably also, the apparatus together with the cannula are implantableinto the living tissue or cavities of the subject.

An embodiment of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a lengthwise cross-section of a pump according to the presentinvention;

FIGS. 2 to 5 are respectively cross-sectional views of the pump alongthe lines II--II, III--III, IV--IV and V--V of FIG. 1, the views beingto the same scale which is larger than that in FIG. 1; and

FIGS. 6A and 6B are respectively a plan view and an end view of anapparatus according to the present invention of a size implantable intothe living tissue or cavities of a subject.

Referring to FIGS. 1 to 5 of the drawings, a pump comprises acylindrical casing 10 whose interior defines an elongate chamber 11. Apiston 12 is co-axially movable in said chamber 11. The piston 12 is anassembly comprising a tube 12A which has on its outside circumferencetwo similar rings 14 integral therewith and spaced apart on and proud ofits surface. Each ring 14 is adjacent to an end of the piston 12. Thelands on the outside of the rings 14 are in sliding engagement with theinside walls of the casing 10. Between the rings 14, pistoncircumference and the inside wall of the casing 10, an annular passage15 is defined. Mid-way of the bore 8 of the tube 12A a square inletvalve magnet 16 is in push-fitted engagement (FIG. 4). Symmetrical aboutthe magnet 16, two similar inlet valves are provided comprising balls17,17' and seats 18,18'. An axially-bored plug 19,19' secures the balls17,17' and seats 18,18' in their positions in the piston. To the outsideend wall of the plugs 19,19', a piston armature 20,20' is secured. Thearmatures 20,20' are bored in axial alignment with the bores in theplugs 19,19' and are both co-axial with the tube 12A and casing 10.Piston lock magnets 9,9' are mounted in axial recesses in outer endwalls of piston armatures 20,20'.

Two fixed cores 21, 21' are symmetrically secured in the opposite endsof the casing 10 leaving air gaps 22, 22' thereby to define the extentof reciprocal movement of the piston 12. Two similar sleeves 23, 23' aresecured around the fixed cores 21, 21' as extensions of the casing 10.The outer ends of the sleeves 23, 23' are closed off by outlet valveplugs 24, 24' having axial bores. In the sleeves 23, 23' between thefixed cores 21, 21' and plugs 24, 24' two valve armatures 25, 25' areslidably movable. The armatures 25, 25' are formed from two materials tobe defined hereinafter secured together the outer parts being 25A, 25A'.Two similar outlet valves are provided comprising balls 27, 27' andoutlet valve seats 26, 26'. The seats 26, 26' are located in axialrecesses and the inner end of plugs 24, 24'. Square outlet valve magnets28, 28' are provided in cylindrical recesses in the outer ends of valvearmatures 25, 25' (FIG. 2). Two electromagnet coils 29, 29' are providedwound respectively around the fixed cores 21, 21' as shown in FIGS. 1and 3 and between collars 30, 30' and 31, 31' and covers 32, 32' areprovided to fit over the outside of the coils 29, 29'. Valve air gaps33, 33' are provided between fixed cores 21, 21' and valve armatures 25,25'.

An annulus 34 is provided around the pump casing 10 and seats in collars30, 30' and an annular passage 35 is defined between said annulus 34 andcasing 10. Annulus 34 has a port 36 to be secured to a reservoir offluid, the port 36 communicating with passage 35. Casing 10 has fourequi-spaced ports 37 allowing fluid communication from passage 35 topassage 15, and tube 12A has four equi-spaced ports 38 allowing fluidcommunication from passage 15 to bore 8.

Annulus 34, sleeves 23, 23', casing 10, plugs 19, 19' and ports 25A,25A' of valve armatures 25, 25' are all of non-magnetic material such anInionel 600, but can be of non-magnetic stainless steels or plastics.The iron path comprises of the collars 30, 30'; 31, 31' and cover 32,32', together with the fixed core 21, 21', the valve armature 25, 25'except parts 25A, 25A' referred to above, and the piston armatures 20,20' are all of a material such as Mu-metal, although other materials forexample Mu-metal plus, Super Mu-metal, Ortho metal, Super Radio metal orPermendor can be used.

The balls 27, 27' and 17, 17' are of Tungsten Carbide, although theycould be of a material such as those used above for the fixed cores 21,21'. The valve seats 26, 26' and 18, 18' are of synthetic sapphire butcan be of ceramics, Inconel 600, non-magnetic stainless steels orplastics. The magnets 16, 9, 9' and 28, 28' are all of sinteredcobalt-samarium but can be of Alnico, platinum cobalt, nialco, reco,conife, or cumico.

Pumping action is achieved by alternately energising the coils 29, 29'of the electromagnets to achieve reciprocation of the piston 12.Induction of fluid is achieved by the two inlet valves whose motion iscontrolled by the hydraulic forces generated by the motion of the piston12. The outlet valves are powered open by electromagnet means. This isachieved by having the fixed core 21, 21' to act as a stop in eachelectromagnet and using a second armature 25, 25' to pull the outletvalve open as the piston is pulled into the electromagnet.

With reference to FIG. 1, the electromagnet coil 29 is energised causingmagnetic flux to set up around the iron path comprised of the collar 30,collar 31 and cover 32, and thus through the valve armature 25, fixedcore 21, and piston armature 20. This causes the piston armature20/piston 12 to abut against the fixed core 21 closing air gap 22 toexhaust a volume of liquid in said air gap equal to the volume of theair gap. The electric power to coil 29 is then switched off. By causingan electric current to flow in electromagnet coil 29', the air gap 22'will be closed to pump liquid. The piston 12 is held in its restposition by the piston locking magnets 9, 9' which are mounted in thepiston armatures 20, 20'. This ensures that the piston 12 will not driftbetween strokes as a result of leaks in the valves or piston seals. Inconsidering the inlet valve assemblies, each valve consists of a balland seat. The ball has magnetic properties similar to iron and the seatsare of non-magnetic material as mentioned above. The balls 17, 17', whenthe valves are not operating, are tensioned against their seats 18, 18'by the inlet valve magnet 16. In FIG. 1, the piston 12 has been pulledacross by piston armature 20 being forced to close air gap 22 by acurrent flowing through electromagnet coil 29. This causes the air gap22' to open creating a negative pressure which is transmitted throughthe axial bore in piston armature 20' and thence to the inlet ball 17'.This hydraulic force overcomes the magnetic force seating the ball 17'and causes fluid to flow from the reservoir through port 36 into passage35 and through ports 37 into passage 15 and thence to fill air gap 22'by the fluid passages provided. Once the pressure is equalised then theball 17' will seat under the influence of the magnetic force from theinlet valve magnet 16.

In considering the outlet valve assemblies, these comprise the valvearmatures 25, 25'. The parts of the armatures to be under the influenceof the solenoids are made from materials similar in magnetic propertiesto iron, the materials being given above. The part of the armaturevalves housing the outlet valve magnets 28, 28' are made fromnon-megnetic material, details of the materials being given above. Thisis to ensure the valve armatures 25, 25' are not held in the energisedposition by stray flux from the magnets 28, 28'.

It would be obvious to one with ordinary skill in the art that since theoutlet valve balls 27,27' are made from a material having ferromagneticproperties they will be attracted to the centre of the face of theoutlet valve magnets 28,28'. It is therefore apparent that they will befree to centralise in the non-magnetic outlet valve seats 26,26'. Thevalves held in the closed position by the outlet valve magnets 28, 28'pulling against the outlet valve plugs 24, 24' which have ferro-magneticproperties. The closing force on the outlet valves greatly exceeds theclosing force on the inlet valves ensuring that they are not moved bythe hydraulic forces operating the inlet valves.

Outlet valve 27 operates as follows: Coil 29 is energised. Before thepiston with piston armatures moves for piston armature 20 to abut fixedcore 21 thereby closing air gap 22, piston armature 20' was againstfixed core 21' and held there by the piston lock magnet 9'. This holdingforce is of the same order as the pull exerted on the valve armature 25by the outlet valve magnet 28 on the outlet valve plug 24. These forcescancel each other out. The valve air gap 33 in its start position isless than the piston air gap 22 in its start position, thus the pull onthe valve armature 25 will exceed that on the piston armature 20ensuring the outlet valve 27 will open to allow fluid to be exhausted.Two hydraulic considerations also ensure that the valve will open. Thefirst part of the force exerted on the piston armature 20 will berequired to unseat the ball valve 17'. Secondly, the hydraulic pressuregenerated by closing air gap 22 will restrain the motion of the piston12 by acting on the area bounded by the seal on the piston. The fluidhas free passage around and through the valve armature 25 so thehydraulic force will be distributed on both faces of this component(less the small area where the ball contact the magnet). The sum of allthese force considerations mean that the outlet valve will open. Outletvalve 27' operates in a similar manner on coil 29' being energised.

The fact that the valves in the pump operate on the same current pulseas the piston allows relatively simple driving circuits. The powering ofthe valves against the flow of liquid through the pump is a safeguardagainst inadvertent flow of liquid. For example, a rise of pressure atthe outlet greater than the pressure which the pump will work into locksthe inlet valve shut.

Similarly, a rise in reservoir pressure will lock the outlet valve whenthe hydrostatic force on the outlet valve ball overcomes the attractiveforce between this member and the outlet valve magnet.

An apparatus for infusing into a subject, namely an animal or humanbeing, determined quantities of liquid medicine at predetermined timeintervals is shown in FIGS. 6A and 6B and comprises a printed circuitbase board 40 having electronic components thereon, a pump as describedabove side-by-side with a reservoir 41, power means 42, a liquid crystalvisual display unit 43, tubing 44 and 45 from both ends of the pump toan outlet 46 to be connected to a cannula (not shown). The reservoir hasa self sealing bung 47 for injecting refil liquid medicine into thereservoir 41. The power means 42 are lithium batteries but mayalternatively be atomic batteries. The apparatus as shown in the FIGS.6A and 6B are actual size for implanting subcutaneously or forpositioning in cavities in a human body. The apparatus may however beportable in the form of a watch to be strapped to the wrist.

Also, the apparatus may be of increased size and usable with existingdrip-feed equipment.

The implantable and wrist strap models are primarily for administeringliquid medicine such as insulin or heparin but can be used for infusingany liquid medicine while the human being is going about normal dailylife.

The coils 29, 29' are of copper wire but for utmost efficiency with thesmaller pumps may be of silver wire, the silver wire version giving onpercentage increase in turns per equivalent copper wire version of 20%.

If the pump is to be frequently pulsed, then piston locking magnets 9,9' could be omitted since there would not be time for leaks to occur.

The pump as described above can be modified without departing from thescope of the invention in the manner as follows:

(a) The passage 35 can be omitted.

(b) The inlet valve seats 18, 18' can be permanent magnets obviating therequirements for inlet valve magnet 18.

(c) The inlet valve balls 17, 17' can be permanent magnets andconsequently the valve seats 18, 18' are of ferromagnetic or permanentmagnetic material.

(d) The non-magnetic plugs 19, 19' can be of the same ferromagneticmaterial as the piston armatures 20, 20'. This will effect a holdingforce between the piston armature 20 or 20' and the fixed core 21 or 21'and so the piston locking magnets 9, 9' can be omitted.

(e) The outlet valve can have the fixed armature secured to its sleeve.In this case, if the sleeve had an outside diameter that fitted insidethe piston armature bore then a screw-thread between them would allowthe stroke of the pump to be altered.

(f) The pump can be single-acting instead of double-acting asabove-described, in which case the pump will comprise one half of thepump described above i.e. as if it is cut along the line IV--IV and aplate of ferromagnetic material is used to effect a fluid seal. Theinlet magnet will then provide a returning force when coil 29 wasswitched off. In this case, the coil 29 would need to provide morepower.

The pump of the invention can be controlled by many forms of electroniccontrol depending on use. For example when used as an implant it mayform part of a closed loop system, controlled by a sensing device. Animportant feature of the pump is that it can easily be interfaced with awide variety of electronics as it responds to intermittent pulsedinformation. Also, it has zero quiescent current consumption, the movingcomponents having the magnets as "memories".

I claim:
 1. A pump comprising a casing defining an elongate chamber,inlet and outlet valves communicating with the chamber, a pistoncoaxially movable in the chamber, and an electromagnet controllingmovement of the piston via an armature, the outlet valve also beingcontrolled by the electromagnet via a valve armature;characterised inthat the inlet and outlet valves are balls made from a material havingferromagnetic properties and seats made of non-magnetic material andmagnets tensioning the balls of said inlet and outlet valves againsttheir seats when in a closed position, and in that power means foropening said balls from their seats, comprise for said inlet valve aforce equivalent to a hydraulic force caused by coaxial movement of thepiston in the chamber, said piston and said outlet valve being operatedagainst the flow of liquid by the excitation of the singleelectromagnet, a piston lock magnet providing a biasing force on thepiston thereby to inhibit unintentional movement of the piston, and saidoutlet valve remaining closed in response to adverse inlet or outletpressure conditions to prevent inadvertent flow of liquid.
 2. A pumpaccording to claim 1, in which a second electromagnet is spaced apartand axially aligned with the first electromagnet, the armatures of bothelectromagnets being oppositely linked together by the piston.
 3. A pumpaccording to claim 2, in which the electromagnets have coils woundaround the casing.
 4. A pump according to claim 3, in which those partsof the casing on which the coils are wound are relatively thin sleevesof non-magnetic material, and each coil is surrounded on its outersurfaces with relatively thick members of low-reluctance magneticmaterial.
 5. An apparatus for infusing into a subject predeterminedquantities of liquid medicine at predetermined time intervals, theapparatus comprising a pump in combination with a reservoir, the pumpcomprising a casing defining an elongate chamber, inlet and outletvalves communicating with the chamber, a piston coaxially movable in thechamber, and an electromagnet controlling movement of the piston via anarmature, the outlet valve also being controlled by the electromagnetvia a valve armature;characterised in that the inlet and outlet valvesare balls made from a material having ferromagnetic properties and seatsmade of non-magnetic material and magnets tensioning the balls of saidinlet and outlet valves against their seats when in a closed position,and in that power means for opening said balls from their seats,comprise for said inlet valve a force equivalent to a hydraulic forcecaused by coaxial movement of the piston in the chamber, said piston andsaid outlet valve being operated against the flow of liquid by theexcitation of the single electromagnet, a piston lock magnet providing abiasing force on the piston thereby to inhibit unintentional movement ofthe piston, and said outlet valve remaining closed in response toadverse inlet or outlet pressure conditions to prevent inadvertent flowof liquid, the pump having an outlet adapted to engage a cannula wherebyliquid pumped from the reservoir may be infused into a subject, andincluding timing means arranged to actuate the piston at predeterminedregular intervals.
 6. An apparatus according to claim 5, in which thepump casing and the reservoir are mounted side-by-side on a printedcircuit board which also carries control circuitry connected to theelectromagnet.